The present invention relates generally to communications systems and networks, and more particularly to systems and methods for providing facility and equipment protection and restoration services in optical networks.
Modern digital telecommunications systems are built upon a hierarchical network. The network consists of a plurality of nodes or sites that are interconnected by transmission facilities. Generally, lower bandwidth level demands are multiplexed into higher bandwidth demands. For example, up to twenty-eight 1.544 Mbps DS1 channels can be multiplexed into a single 4.376 Mbps DS3 channel. Similarly, up to twelve DS3 channels can be multiplexed into a single 622.08 Mbps OC12 channel. Finally, up to sixteen OC12 channels can be multiplexed into a single 9.953 Gbps OC192 channel. Since a DS1 channel can carry up to twenty four telephone conversations, a single OC192 channel can carry over one hundred thousand telephone conversations.
A telecommunications network consists of equipment, which includes transmitters, receivers, and switches, and facilities, which includes the physical transport medium and regeneration and restoration devices. Because of the tremendous volume of calls carried on each channel, it is necessary, in the event of a facility or equipment failure, that service is not interrupted for any significant amount of time.
Typical communications networks have a mesh topology, in which there are alternative paths through the network between nodes. Accordingly, when there is a facility failure, as for example, when an optical fiber is cut, there is a separate path to which the traffic on the cut fiber can be switched. Today, when a cut occurs, traffic is rerouted at the DS3 level through other sites so that the origin and destination are again connected. Since one OC192 fiber connection includes 192 DS3 electrical connections, tremendous broadband digital cross-connect port capacity is required for restoration. Also, switching at the DS3 level is relatively slow.
Accordingly, it is an object of the present invention to provide protection and restoration services in the optical layer of an optical network.
An optical network according to the present invention includes a first optical cross-connect with a plurality of input ports and a plurality of output ports. The network includes a plurality of working channel optical transmitters, each including an optical signal output connected to an input port of the first optical cross-connect and a signal input. Each of the working channel optical transmitters is adapted to transmit an optical signal in a unique wavelength channel. The first optical cross-connect includes an optical measurement device at each of its input ports to sense a loss of signal at any of its input ports.
The network also includes a second optical cross-connect with a plurality of input ports and a plurality of output ports. The second optical cross-connect includes an optical measurement device at each of its input ports to sense a loss of signal at any of its input ports. A plurality of working channel optical receivers, each including an optical signal input, are connected to output ports of the second optical cross-connect. Each of the working channel receivers is adapted to receive an optical signal on one of the working channels.
The first and second optical cross-connects are interconnected by a primary route and a secondary route. The primary and secondary routes each include a wavelength division multiplexer and a wavelength division demultiplexer. Each wavelength division multiplexer includes plurality of optical inputs and one optical output. Each wavelength division demultiplexer includes one optical input and a plurality of optical outputs. The output of each multiplexer is connected to the input of a demultiplexer by optical fiber.
The network includes at least one protection channel optical transmitter that includes a signal input and an optical signal output, and a protection channel optical receiver including an optical signal input and a signal output. The optical signal output of the protection channel transmitter is connected to the first optical cross-connect and the optical signal input of the protection channel receiver is connected to the second optical cross-connect. The protection channel is adapted to carry signals in the event of a working channel transmitter or receiver failure.
In one embodiment of the present invention, the protection channel transmitter and receiver are connected transmit the protection channel on a unique wavelength over the secondary route. The secondary route includes amplification stations, each of which includes a regenerator dedicated to the protection channel. In the event of failure of the primary route, the signal of one of the working channels is transmitted on the protection channel and optical cross-connects are operated to switch the other working channels from the primary routee to the secondary route.
In an alternative embodiment of the present invention, the protection channel occupies a unique wave length, but the network includes means for converting the wavelength of the protection channel to the wavelength of a failed working channel transmitter. Transmitter and receiver are connected to the primary route through the first and second optical cross-connects, respectively.
The network includes a first protection switch controller associated with the first optical cross-connect, and a second protection switch controller associated with second first optical cross-connect. The first protection switch controller is in communication with the first optical cross-connect, the working channel transmitters, and the protection channel transmitter through a local area network. Similarly, the second protection switch controller is in communication with the second optical cross-connect, the working channel receivers, and the protection channel receiver through a local area network. The protection switch controllers are in communication with each other through a wide area network.
The protection switch controllers monitor the network for failures and take action to correct detected failures. For example, when an optical measurement device at an input port of the first optical cross-connect detects a loss of signal, which indicates the failure of a working channel transmitter, the first protection switch controller switches the input signal from the failed transmitter to the protection channel transmitter and notifies the second protection switch controller of the switch. When a loss of signal or an alarm indication signal is detected at the receiving end of the network, the second protection switch controller operates the second optical cross-connect to connect the working channel receivers to the secondary route and notifies the first protection switch controller to operate the first optical cross-connect to switch the working channel transmitters to the secondary route.
In the alternative embodiment of the invention, the protection switch controllers each include an optical signal input connected to an output port of its associated cross-connect and an optical signal output connected to an input port of the cross-connect. Each protection switch controller includes a frequency converter that converts optical signals between the wavelength of the protection channel and the wavelength of a failed channel.
When the first protection switch controller detects a working channel transmitter failure, the first protection switch controller switches the input signal from the failed transmitter to the protection channel transmitter and operates the first optical cross-connect to switch the output of the protection channel transmitter to the optical input of the protection switch controller. The first protection switch controller converts the wavelength of the signal to that of the failed transmitter channel and operates the first optical cross-connect to connect the output of the first protection switch controller to the primary route.